Battery packs having a plurality of primary cells or secondary cells and a wiring circuit board housed in a battery case are widely used. If the electrolyte leaks from any of the cells in such a battery pack, it can corrode the wiring of the wiring circuit board, which can interrupt conduction or, conversely, can lead to a short. In view of this, it has been proposed that an absorbent member equipped with a liquid absorbent capable of absorbing electrolyte be disposed at or near locations of contact with the cells inside the battery pack so that the above-mentioned problems of corrosion and shorting will not occur (Japanese Patent Application Laid-Open No. 2001-351588). A variety of polymer materials can be used as the liquid absorbent here, such as adsorptive types, gelling types, and self-swelling types. Specific examples include polyacrylate-based water-absorbent resins, starch-grafted copolymer-based water-absorbent resins, polyvinyl alcohol-based water-absorbent resins, polyacrylamide-based water-absorbent resins, isobutylene/maleic acid copolymer-based water-absorbent resins, long-chain alkyl acrylate crosslinked polymers, and polynorbornenes.
However, these liquid absorbents had the problem of not adequately absorbing carbonate-based solvents, such as propylene carbonate or ethylene carbonate, which are widely used in the non-aqueous electrolyte battery packs that have become so popular in recent years, and particularly in the non-aqueous electrolyte secondary cells that constitute a lithium ion nonaqueous electrolyte rechargeable battery pack.
It is an object of the present invention to solve these problems encountered with the prior art, and to provide a liquid-absorbent composition and liquid-absorbent sheet containing a liquid-absorbent crosslinked resin that exhibits excellent absorption of the nonaqueous electrolyte of nonaqueous electrolyte secondary cells that constitute a nonaqueous electrolyte battery pack (and particularly a lithium ion nonaqueous electrolyte rechargeable battery pack), and to provide a method for manufacturing such a liquid-absorbent crosslinked resin, and to provide a battery pack comprising an electrolyte absorption member formed from such a liquid-absorbent composition or liquid-absorbent sheet.